The present invention relates to wire stents and related vascular devices. More particularly, it refers to a stent or other vascular positioned device containing a wire coated with a biocompatible fluoropolymer.
My prior application includes stents made from interwoven groups of yarn filaments containing a wire. See U.S. patent application Ser. No. 09/108,774, filed Jul. 2, 1998, herein incorporated by reference. In addition, U.S. Pat. No. 5,961,545 describes wire stents immobilized longitudinally between tubes of expandable polytetrafluoroethylene. U.S. Pat. No. 5,957,954 describes braiding a stent and a polytetrafluoroethylene textile strand sleeve together in an axial alignment. U.S. Pat. No. 6,015,432 describes an endovascular tube made from woven graft material with a wire employed in openings in the weave. U.S. Pat. No. 5,741,325 describes a self-expanding intraluminal prosthesis containing interwoven fibers including reinforcing wire. U.S. Pat. No. 5,607,478 describes how to make a prosthesis from an expanded polytetrafluoroethylene tube (ePTFE) with a winding of PTFE.
It also is well known in the prior art to coat insulated wire with foamed fluoropolymer insulation as described in U.S. Pat. No. 5,770,819. None of these prior art disclosures teach how to coat a wire used in a prosthesis with a porous expanded PTFE to create uniform expansion of the prosthesis.
I have now invented a process to improve my stent of U.S. application Ser. No. 09/108,774 by coating multiple interlaced wire strands with a porous expanded PTFE. The addition of expanded PTFE to the wire strand reduces platelet adhesion to the stent product. Restenosis will not occur since tissue and cells will not adhere to the expanded PTFE.
The process of this invention is achieved by pretreating a spool of wire to achieve a predetermined shape to the wire and returning the treated wire to its spool. The wire is then fed into an ePTFE extrusion machine where the wire feed is regulated depending on the speed of the extrusion machine. The wire is fed first into a nozzle of the extruder, the nozzle having a concentric opening in which the ePTFE is heated, sintered and then extruded. A laser determines the thickness of the ePTFE layer to maintain uniformity on the wire. The ePTFE coated wire is then respooled and interlaced by braiding or knitting with other coated wire. Various angles are formed with the coated wire which determines the radial and axial compressibility of the resulting stent.